Zero-day vulnerability

Template:Short description A zero-day (also known as a 0-day) is a vulnerability or security hole in a computer system unknown to its developers or anyone capable of mitigating it. Until the vulnerability is remedied, threat actors can exploit it in a zero-day exploit, or zero-day attack.

The term "zero-day" originally referred to the number of days since a new piece of software was released to the public, so "zero-day software" was obtained by hacking into a developer's computer before release. Eventually the term was applied to the vulnerabilities that allowed this hacking, and to the number of days that the vendor has had to fix them. Vendors who discover the vulnerability may create patches or advise workarounds to mitigate it – though users need to deploy that mitigation to eliminate the vulnerability in their systems. Zero-day attacks are severe threats.

Definition

Despite developers' goal of delivering a product that works entirely as intended, virtually all software and hardware contain bugs.Template:Sfn If a bug creates a security risk, it is called a vulnerability. Vulnerabilities vary in their ability to be exploited by malicious actors. Some are not usable at all, while others can be used to disrupt the device with a denial of service attack. The most valuable allow the attacker to inject and run their own code, without the user being aware of it.Template:Sfn Although the term "zero-day" initially referred to the time since the vendor had become aware of the vulnerability, zero-day vulnerabilities can also be defined as the subset of vulnerabilities for which no patch or other fix is available.Template:SfnTemplate:SfnTemplate:Sfn A zero-day exploit is any exploit that takes advantage of such a vulnerability.Template:Sfn

Exploits

An exploit is the delivery mechanism that takes advantage of the vulnerability to penetrate the target's systems, for such purposes as disrupting operations, installing malware, or exfiltrating data.Template:Sfn Researchers Lillian Ablon and Andy Bogart write that "little is known about the true extent, use, benefit, and harm of zero-day exploits".Template:Sfn Exploits based on zero-day vulnerabilities are considered more dangerous than those that take advantage of a known vulnerability.Template:SfnTemplate:Sfn However, it is likely that most cyberattacks use known vulnerabilities, not zero-days.Template:Sfn

Governments of states are the primary users of zero-day exploits, not only because of the high cost of finding or buying vulnerabilities, but also the significant cost of writing the attack software. Nevertheless, anyone can use a vulnerability,Template:Sfn and according to research by the RAND Corporation, "any serious attacker can always get an affordable zero-day for almost any target".Template:Sfn Many targeted attacksTemplate:Sfn and most advanced persistent threats rely on zero-day vulnerabilities.Template:Sfn

The average time to develop an exploit from a zero-day vulnerability was estimated at 22 days.Template:Sfn The difficulty of developing exploits has been increasing over time due to increased anti-exploitation features in popular software.Template:Sfn

Window of vulnerability

File:Vulnerability timeline.png

Vulnerability timeline

Zero-day vulnerabilities are often classified as alive—meaning that there is no public knowledge of the vulnerability—and dead—the vulnerability has been disclosed, but not patched. If the software's maintainers are actively searching for vulnerabilities, it is a living vulnerability; such vulnerabilities in unmaintained software are called immortal. Zombie vulnerabilities can be exploited in older versions of the software but have been patched in newer versions.Template:Sfn

Even publicly known and zombie vulnerabilities are often exploitable for an extended period.Template:SfnTemplate:Sfn Security patches can take months to develop,Template:Sfn or may never be developed.Template:Sfn A patch can have negative effects on the functionality of softwareTemplate:Sfn and users may need to test the patch to confirm functionality and compatibility.Template:Sfn Larger organizations may fail to identify and patch all dependencies, while smaller enterprises and personal users may not install patches.Template:Sfn

Research suggests that risk of cyberattack increases if the vulnerability is made publicly known or a patch is released.Template:Sfn Cybercriminals can reverse engineer the patch to find the underlying vulnerability and develop exploits,Template:Sfn often faster than users install the patch.Template:Sfn

According to research by RAND Corporation published in 2017, zero-day exploits remain usable for 6.9 years on average,Template:Sfn although those purchased from a third party only remain usable for 1.4 years on average.Template:Sfn The researchers were unable to determine if any particular platform or software (such as open-source software) had any relationship to the life expectancy of a zero-day vulnerability.Template:Sfn Although the RAND researchers found that 5.7 percent of a stockpile of secret zero-day vulnerabilities will have been discovered by someone else within a year, another study found a higher overlap rate, as high as 10.8 percent to 21.9 percent per year.

Countermeasures

Because, by definition, there is no patch that can block a zero-day exploit, all systems employing the software or hardware with the vulnerability are at risk. This includes secure systems such as banks and governments that have all patches up to date.Template:Sfn Security systems are designed around known vulnerabilities, and repeated exploitations of a zero-day exploit could continue undetected for an extended period of time.Template:Sfn Although there have been many proposals for a system that is effective at detecting zero-day exploits, this remains an active area of research in 2023.Template:Sfn

Many organizations have adopted defense-in-depth tactics so that attacks are likely to require breaching multiple levels of security, which makes it more difficult to achieve.Template:Sfn Conventional cybersecurity measures such as training and access control such as multi-factor authentication, least-privilege access, and air-gapping makes it harder to compromise systems with a zero-day exploit.Template:Sfn Since writing perfectly secure software is impossible, some researchers argue that driving up the cost of exploits is a good strategy to reduce the burden of cyberattacks.Template:Sfn

Market

Zero-day exploits can fetch millions of dollars.Template:Sfn There are three main types of buyers:Template:Sfn

• White: the vendor, or to third parties such as the Zero Day Initiative that disclose to the vendor. Often such disclosure is in exchange for a bug bounty.Template:SfnTemplate:SfnTemplate:Sfn Not all companies respond positively to disclosures, as they can cause legal liability and operational overhead. It is not uncommon to receive cease-and-desist letters from software vendors after disclosing a vulnerability for free.Template:Sfn
• Gray: the largestTemplate:Sfn and most lucrative. Government or intelligence agencies buy zero-days and may use it in an attack, stockpile the vulnerability, or notify the vendor.Template:Sfn The United States federal government is one of the largest buyers.Template:Sfn As of 2013, the Five Eyes (United States, United Kingdom, Canada, Australia, and New Zealand) captured the plurality of the market and other significant purchasers included Russia, India, Brazil, Malaysia, Singapore, North Korea, and Iran. Middle Eastern countries were poised to become the biggest spenders.Template:Sfn
• Black: organized crime, which typically prefers exploit software rather than just knowledge of a vulnerability.Template:Sfn These users are more likely to employ "half-days" where a patch is already available.Template:Sfn

In 2015, the markets for government and crime were estimated at at least ten times larger than the white market.Template:Sfn Sellers are often hacker groups that seek out vulnerabilities in widely used software for financial reward.Template:Sfn Some will only sell to certain buyers, while others will sell to anyone.Template:Sfn White market sellers are more likely to be motivated by non pecuniary rewards such as recognition and intellectual challenge.Template:Sfn Selling zero-day exploits is legal.Template:Sfn Despite calls for more regulation, law professor Mailyn Fidler says there is little chance of an international agreement because key players such as Russia and Israel are not interested.

The sellers and buyers that trade in zero-days tend to be secretive, relying on non-disclosure agreements and classified information laws to keep the exploits secret. If the vulnerability becomes known, it can be patched and its value consequently crashes.Template:Sfn Because the market lacks transparency, it can be hard for parties to find a fair price. Sellers might not be paid if the vulnerability was disclosed before it was verified, or if the buyer declined to purchase it but used it anyway. With the proliferation of middlemen, sellers could never know to what use the exploits could be put.Template:Sfn Buyers could not guarantee that the exploit was not sold to another party.Template:Sfn Both buyers and sellers advertise on the dark web.Template:Sfn

File:Comparing the average prices of different kinds of exploits, from 2015 until present.png

Comparing the average prices of different kinds of exploits, 2015–2022

Research published in 2022 based on maximum prices paid as quoted by a single exploit broker found a 44 percent annualized inflation rate in exploit pricing. Remote zero-click exploits could fetch the highest price, while those that require local access to the device are much cheaper.Template:Sfn Vulnerabilities in widely used software are also more expensive.Template:Sfn They estimated that around 400 to 1,500 people sold exploits to that broker and they made around $5,500 to $20,800 annually.

Disclosure and stockpiling

since 2017Template:Dated maintenance category (articles), there is an ongoing debate as to whether the United States should disclose the vulnerabilities it is aware of, so that they can be patched, or keep them secret for its own use.Template:Sfn Reasons that states keep a vulnerability secret include wanting to use it offensively, or defensively in penetration testing.Template:Sfn Disclosing the vulnerability reduces the risk that consumers and all users of the software will be victimized by malware or data breaches.Template:Sfn

The phases of zero-day vulnerability disclosure, along with a typical timeline, are as follows:

1. Discovery: A researcher identifies the vulnerability, marking "Day 0."
2. Reporting: The researcher notifies the vendor or a third party, starting remediation efforts.
3. Patch development: The vendor develops a fix, which can take weeks to months depending on the complexity.
4. Public disclosure: Once a patch is released, details are shared publicly. If no patch is issued within an agreed period (commonly 90 days), some researchers disclose it to push for action.

History

Zero-day exploits increased in significance after services such as Apple, Google, Facebook, and Microsoft encrypted servers and messages, meaning that the most feasible way to access a user's data was to intercept it at the source before it was encrypted.Template:Sfn One of the best-known use of zero-day exploits was the Stuxnet worm, which used four zero-day vulnerabilities to damage Iran's nuclear program in 2010.Template:Sfn The worm showed what could be achieved by zero-day exploits, unleashing an expansion in the market.Template:Sfn

The United States National Security Agency (NSA) increased its search for zero-day vulnerabilities after large tech companies refused to install backdoors into the software, tasking the Tailored Access Operations (TAO) with discovering and purchasing zero-day exploits.Template:Sfn In 2007, former NSA employee Charlie Miller publicly revealed for the first time that the United States government was buying zero-day exploits.Template:Sfn Some information about the NSA involvement with zero-days was revealed in the documents leaked by NSA contractor Edward Snowden in 2013, but details were lacking.Template:Sfn Reporter Nicole Perlroth concluded that "either Snowden’s access as a contractor didn’t take him far enough into the government’s systems for the intel required, or some of the government’s sources and methods for acquiring zero-days were so confidential, or controversial, that the agency never dared put them in writing".Template:Sfn

One of the most infamous vulnerabilities discovered after 2013, Heartbleed (CVE-2014-0160), was not a zero-day when publicly disclosed but underscored the critical impact that software bugs can have on global cybersecurity. This flaw in the OpenSSL cryptographic library could have been exploited as a zero-day prior to its discovery, allowing attackers to steal sensitive information such as private keys and passwords.

In 2016 the hacking group known as The Shadow Brokers released a trove of sophisticated zero-day exploits reportedly stolen from the NSA. These included tools such as EternalBlue, which leveraged a vulnerability in Microsoft Windows' Server Message Block (SMB) protocol. EternalBlue was later weaponized in high-profile attacks like WannaCry and NotPetya, causing widespread global damage and highlighting the risks of stockpiling vulnerabilities.

The year 2020 saw one of the most sophisticated cyber espionage campaigns to date, in which attackers exploited multiple vulnerabilities, including zero-day vulnerabilities, to compromise SolarWinds' Orion software. This allowed access to numerous government and corporate networks.

In 2021 Chinese state-sponsored group, Hafnium, exploited zero-day vulnerabilities in Microsoft Exchange Server to conduct cyber espionage. Known as ProxyLogon, these flaws allowed attackers to bypass authentication and execute arbitrary code, compromising thousands of systems globally.

In 2022 the spyware Pegasus, developed by Israel's NSO Group, was found to exploit zero-click vulnerabilities in messaging apps like iMessage and WhatsApp. These exploits allowed attackers to access targets' devices without requiring user interaction, heightening concerns over surveillance and privacy.